Noise, Vibration, and Harshness (NVH) behavior of a vehicle is significantly influenced by the vehicle's powertrain. For example, NVH may result from vibration due to combustion quality issues, torque converter operation, and variable displacement cylinder switching. For example, cylinder deactivation causes lower frequency and higher amplitude torque vibrations at the crankshaft. These vibrations can be transmitted through components such as seats, steering wheel etc., to the vehicle occupants, thereby generating undesirable noise within the vehicle cabin. Further, transmissions experience noises such as gear meshing noise and pump noise. Furthermore, gasoline engines experience noise from sources such as direct-injection fuel systems. Example methods to control NVH include coordinately controlling the noise through electronically controlled devices to provide smooth consistent operation. In some examples, in order to improve NVH, engine-operating modes, such as variable displacement, are limited to certain engine operating regions, such as mid-range engine speeds at low or moderate loads.
However, the inventors have recognized that the methods that limit NVH also have a negative impact on fuel economy. In other words, when NVH constraints are imposed, fuel economy improvement is reduced. As a result, there is a trade-off between NVH and fuel economy, and the NVH limit becomes the limit for fuel economy improvement that a given technology can provide. For example, as described previously, operating range of fuel saving technologies, such as VDE, is limited due to NVH constraints. Consequently, the fuel economy improvement that can be achieved with it is also reduced. Further, it is assumed that an occupant will be in the vehicle 100% of the time the vehicle is moving, and thus, the NVH limit for a given operation is set and does not change during the life cycle of the vehicle.
Furthermore, the inventors have recognized that in vehicles with autonomous capabilities, the assumption that an occupant will be in the vehicle does not hold. For example, the vehicle may be operated in an autonomous mode without any occupant between passenger pick-up locations or while transferring goods. When no occupants are present, the active controls to limit NVH severely impact fuel economy without actually providing driver comfort. For example, NVH related constraints depend on human perception (e.g., through seat, steering, pedal, and audible perception for a driver; through seat and audible perception for a passenger). These constraints are no longer applicable in the absence of occupants; yet, the NVH constraints affect fuel economy improvement.
In one example, the issues described above may be addressed by a method for operating a vehicle, comprising: during an autonomous mode of vehicle operation, altering noise, vibration, and harshness (NVH) limits for a powertrain of the vehicle responsive to detecting zero occupants within the vehicle to improve fuel economy. In this way, drivability may be compromised when zero occupants are detected within the vehicle in order to improve fuel economy.
As one example, when a vehicle is operating in autonomous mode, if zero occupants are detected within the vehicle, NVH constraints limiting fuel economy for a given technology may be relaxed in order to improve fuel economy. For example, with reduced NVH constraints, operating range of one or more of variable displacement operation, deceleration fuel shut off, exhaust gas recirculation, may be expanded to provide greater fuel economy improvement while compromising NVH. Further, torque converter slip may be adjusted towards less slip to improve fuel economy by reducing torque loss. Furthermore, transmission shift schedule may be adjusted for improved fuel economy. As a result, the vehicle will improve fuel economy at the expense of NVH. However, the NVH will not drive customer complaints through interaction, as there are no occupants in the vehicle. In this way, by setting different NVH limits or constraints based on whether an occupant is present or not, fuel saving technologies, such as variable displacement operation, DFSO, etc., may be maximized for fuel economy improvement.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.